A potassium channel activated by calcium is expressed in various animal cells, and plays an important role in the regulation of cell functions. That is, the potassium channel activated by calcium performs potassium excretion by opening the channel in response to an increase in intracellular calcium in excitable and non-excitable cells, and regulates membrane potentials by inducing after-hyperpolarization. The potassium channel activated by calcium is classified as a large conductance channel (BK), a small conductance channel (SK), and an intermediate conductance channel (IK). In these channels, it was confirmed that the IK channel is expressed in lymphocytes, red blood cells, fibroblasts, vascular endothelial cells, airway epitheliums, an gastrointestinal tract, peripheral nerves, dorsal root ganglions, and the like and it was suggested that the IK channel is involved in diseases which target these (Current Medicinal Chemistry, 2007, vol. 14, p. 1437-1457). In addition, from the fact that it was reported that the IK1/SK dual opener improves visceral hypersensitivity and abnormal bowel movement (Gastroenterology, 2008, vol. 134, Issue 4, Supplement 1, p. A-544, T1386), a possibility of treatment for irritable bowel syndrome (IBS) was suggested.
On the other hand, there is a report that the IK1 channel is expressed in the sensory nervous system, but there is no change in the expression level in a neuropathic pain model and an inflammatory pain model (Neuroscience, 2005, vol. 131, p. 161-175) and a report that the IK1 is involved in the analgesic action of a PPAR agonist (The Journal of Pharmacology and Experimental Therapeutics, 2006. vol. 319, p. 1051-1061). However, a certain view has not been obtained for the relationship between the IK1 channel and a pain disorder. Furthermore, there has been no report showing that the IK1 channel activator is effective in inflammatory pain, osteoarthritis pain, neuropathic pain, or fibromyalgia, using disease animal models.